This application is based upon and claims priority from prior French Patent Application No. 99-07110, filed Jun. 4, 1999, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to equipment networks, and more specifically to methods for communicating on an equipment network.
2. Description of Related Art
An equipment network is an arbitrary group of equipment units that are connected together by any link so as to allow the exchange of information messages, control messages, and/or energy. The equipment units can be domestic appliances in a home management network, computers in a data processing network, urban equipment such as street lights that are connected to a control center, meteorological recording units, telephone repeaters, television repeaters, or the like. The linking equipment can be a LAN-type current carrier computer network (local area network), a coaxial cable or fiber-optic network, or air or another physical medium when transmitting through electromagnetic waves (e.g., using radio frequency or optical transmission).
Conventionally, there are two types of networks that can be distinguished as a function of the spatial arrangement of the equipment. First, there are xe2x80x9cstandardizedxe2x80x9d networks in which the distance separating two equipment units in the network is known during equipment design and installation. For example, this is the case in a network of line repeaters for sending long distance telephone signals. The repeaters are separated from one another by a constant or approximately constant distance. Additionally, there are xe2x80x9cnon-standardizedxe2x80x9d networks in which the distance separating two equipment units is not defined in advance. For example, this is the case in a network of domestic appliances connected in a ring inside a home. The journey of the exchanged messages and the distance traveled by these messages between two equipment units are not known during equipment manufacture and/or network installation.
FIG. 1 is a diagram showing a network of equipment units E1 to E6 that are configured in a ring and connected through linking means LT to each other and to a specialized equipment unit CU that is a control unit. The network is a nonstandardized network in which the distance between two equipment units E1-E6 and between the equipment units E1-E6 and the control unit CU is unknown. The messages sent by one equipment unit (i.e., the sending unit) to another equipment unit (i.e., the receiving unit) are sent in the form of a signal such as a modulated electrical signal.
In such a non-standardized network, the messages are sent with a nominal power level Un that is independent of the distance separating the sending unit from the receiving unit. The value of Un is limited by considerations concerning economic electrical power consumption, power supply capabilities of the sending unit, and electromagnetic compatibility (e.g., a signal, whatever its nature, cannot legally be sent at a very high power without conforming to standards that are established to protect other electrical or electronic devices operating in the same geographical area).
In the network of FIG. 1, a message from equipment unit E3 to the control unit CU passes through equipment units E2, E4, and E6. Because of the attenuation on the linking means, the power level of the signal decreases as the signal advances along the network. For example, the signal may be 0.90xc3x97Un at equipment unit E2, 0.60xc3x97Un at equipment unit E1, 0.40xc3x97Un at equipment unit E6, and finally 0.25xc3x97Un, when it arrives at the control unit CU. Additionally, because of interference effects suffered by signals on the linking means LT, the power level of the signal that is received by the receiving unit may be insufficient for an error-free decoding of the message. In other words, the message may suffer from interference before being received by the receiving unit due to electromagnetic perturbations or the like along the linking means. A similar problem arises in standardized networks when signal attenuation on the linking means varies in an uncontrolled manner.
To overcome this problem, it has been proposed to amplify the signal bearing the transmitted message one or more times (depending on specific requirements) between the sending unit and the receiving unit. This is the principle of signal repeaters. Such an approach improves the signal-to-noise ratio SNR, which is the ratio of the signal power level to the noise power level. In standardized networks, amplification is typically selective insofar as it is only carried out when necessary (i.e., when the power level of the signal received by a given equipment unit during transmission toward the receiving unit, possibly via another intermediate equipment unit, is below a threshold).
However, a drawback exists because this can cause the signal level received by the receiving unit to be relatively high, even though previously in the transmission process the signal level was very low, possibly even close to the noise floor. Thus, despite the fact that the receiving unit sees such a high level, the received message is still susceptible to having been corrupted during transmission. In other words, the fact that the signal was previously amplified so that it is received by the receiving unit at a power level that is not far from Un can mask the risk of corruption in the received message.
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a method for communicating on an equipment network through linking means. A message sent from one equipment unit to another equipment unit as a signal having a nominal power is selectively modified in order to indicate when the signal has been amplified by an intermediate equipment item through which the signal passes. Thus, when received by the receiving equipment unit, the message carries an indication of whether a signal amplification has taken place during transit. This can be used as an indirect indication that the message may have been corrupted so as to contain errors.
One embodiment of the present invention provides a method for communicating on an equipment network through linking means. The equipment network includes equipment units, at least some of which are able to send and/or receive messages. According to the method, a message is sent from a sending equipment unit to a receiving equipment unit as a signal having a nominal power. Whenever the signal is amplified by an intermediate equipment unit through which the signal passes, the message is modified to indicate that the signal has been amplified by the intermediate equipment unit. In a preferred method, the message is modified by incrementing the value of an information word of the message.
Another embodiment of the present invention provides a first equipment unit for connection to an equipment network that connects the first equipment unit and other equipment units through linking means. The first equipment unit includes a receiver for receiving a signal that was sent by a sending equipment unit at a nominal power level, means for measuring data representative of a quality of the received signal, means for comparing the measured data with a first threshold, means for amplifying the signal when the measured data is below the first threshold, means for modifying a message carried by the signal so as to indicate that the signal has been amplified whenever the signal is amplified by the means for amplifying, and a transmitter for sending the signal on to a receiving equipment unit. In one preferred embodiment, the means for comparing also compares the measured data with a second threshold, and the transmitter does not send the signal on to the receiving one of the equipment units when the measured data is below the second threshold.
Yet another embodiment of the present invention provides a message that is sent as a signal from a sending equipment unit of an equipment network to a receiving equipment unit of the equipment network. The message includes an information word having a value that indicates the number of times that the signal has been amplified by intermediate equipment units located on the network between the sending equipment unit and the receiving equipment unit. In a preferred embodiment, the message also includes at least one word that identifies which intermediate equipment units have amplified the signal.